Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.26	3.261%	$57.062	$57.06	$57.05	$57.10
Purchase #2	$92.68	6.840%	$99.0193	$99.02	$99.00	$99.00
Purchase #3	$55.79	6.559%	$59.4493	$59.45	$59.45	$59.40
Purchase #4	$191.76	13.373%	$217.4041	$217.40	$217.40	$217.40
Purchase #5	$44.50	8.429%	$48.2509	$48.25	$48.25	$48.30
Purchase #6	$102.68	13.402%	$116.4412	$116.44	$116.45	$116.40
Purchase #7	$225.74	8.270%	$244.4087	$244.41	$244.40	$244.40
7 purchase totals =	$768.41		$842.0355	$842.03	$842.00	$842.00